Cleaning solution for removing silvercontaining deposits from photographic processing equipment

ABSTRACT

AN AQUEOUS CLEANING SOLUTION FOR REMOVAL OF SILVER-CONTAINING DEPOSITS FROM PHOTOGRAPHIC PROCESSING EQUIPMENT IS COMPRISED OF WATER-SOLUBLE FERRICYANIDE, THIOCYANATE, DICHROMATE, NITRATE AND CITRATE SALTS, A POLYAMINOPOLYACETIC ACID SEQUESTERING AGENT, AND A STRONG INORGANIC BASE. THE CLEANING SOLUTION IS EFFECTIVE IN REMOVING SCALE COMPRISED OF METALLIC SILVER, GELATIN AND HARD WATER SALTS AND IS ESPECIALLY USEFUL IN CLEANING EQUIPMENT EMPLOYED IN PHOTOGRAPHIC PROCESSING SYSTEMS WHICH UTILIZE MONOBATHS.

AU 165 EX 3,586,631 CLEANING SOLUTION FOR REMOVING SILVER- CONTAINING DEPOSITS FROM PHOTOGRAPHIC PROCESSING EQUIPMENT Henry J. Fassbender, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed Sept. 25, 1969, Ser. No. 861,171 Int. Cl. C11d 7/54 US. Cl. 252-103 7 Claims ABSTRACT OF THE DISCLOSURE An aqueous cleaning solution for removal of silver-containing deposits from photographic processing equipment is comprised of water-soluble ferricyanide, thiocyanate, dichromate, nitrate and citrate salts, a polyaminopolyacetic acid sequestering agent, and a strong inorganic base. The cleaning solution is effective in removing scale comprised of metallic silver, gelatin and hard water salts and is especially useful in cleaning equipment employed in photographic processing systems which utilize monobaths.

This invention relates in general to the photographic art and in particular to a novel aqueous cleaning solution for removal of silver-containing deposits from photographic processing equipment.

In the processing of gelatine/silver halide photographic materials, one of the problems encountered is the formation of deposits on the processing equipment which are difficult to remove. These deposits are primarily composed of gelatin and metallic silver but frequently also contain hard water salts, i.e. salts of calcium or magnesium ions present in the water used informulating the processing baths, as well as minor amounts of other materials. Conventional industrial or household cleaning products are ineffective in removing such deposits and removal by scraping is laborious costly and ineffective procedure. This is a particularly serious problem in photographic processing systems which utilize monobaths, i.e. solutions for combining development and fixing, as such systems are particularly susceptible to the formation of deposits which are very difficult to remove. The accumulation of scale on the rollers, racks, trays, tanks, pumps and hoses of the processing machines used in these systems causes serious operating problems, such as inadequate clearance between rollers, plugging of hoses and pumps, and scratching or other physical damage to the photographic materials being processed.

In accordance with this invention, there is provided an aqueous cleaning solution which will effectively remove silver-containing deposits from photographic processing equipment. This cleaning solution is comprised of watersoluble ferricyanide, thiocyanate, dichromate, nitrate and citrate salts, a polyaminopolyacetic acid sequestering agent, and a strong inorganic base. It has been found to work rapidly and efliciently in removing deposits in which metallic silver, gelatin and various salts, such as calcium or magnesium salts resulting from the use of hard water in formulating the processing solutions, are present in varying proportions.

More specifically, the cleaning solution of this invention is an aqueous solution consisting essentially of the following ingredients:

(1) Ammonium ferricyanide or an alkali metal ferricyanide, such as sodium ferricyanide, or potassium ferricyanide, in a concentration of from about 40 to about 200 grams per liter of solution. The preferred concentration range for the ferricyanide is from about 60 to about 100 grams per liter of solution and optimum results are ob- 3,586,631 Patented June 22, 1971 ice tained with a concentration of about grams per liter of solution.

(2) Ammonium thiocyanate or an alkali metal 'thiocyanate, such as sodium thiocyanate or potassium thiocyanate, in a concentration of from about 40 to about 200 grams per liter of solution. The preferred concentration range for the thiocyanate is from about to about 140 grams per liter of solution and optimum results are obtained with a concentration of about grams per liter of solution.

(3) Ammonium dichromate or an alkali metal dichromate, such as sodium dichromate or potassium dichromate, in a concentration of from about 2 to about 25 grams per liter of solution. The preferred concentration range for the dichromate is from about 5 to about 15 grams per liter of solution and optimum results are obtained with about 10 grams per liter of solution.

(4) Ammonium nitrate or an alkali metal nitrate, such as sodium nitrate or potassium nitrate, in a concentration of from about 10 to about 60 grams per liter of solution. The preferred concentration range for the nitrate is from about 20 to about 40 grams per liter of solution and optimum results are obtained with about 30 grams per liter of solution.

(5) Ammonium citrate or an alkali metal citrate, such as sodium citrate or potassium citrate, in a concentration of from about 2 to about 25 grams per liter of solution. The preferred concentration range for the citrate is from about 5 to about 15 grams per liter of solution and optimum results are obtained with about 10 grams per liter of solution.

(6) A polyaminopolyacetic acid sequestering agent in a concentration of from a out 2 to about 20 grams perliter of solution. The preferred concentration range forthe polyamino-polyacetic acid sequestering agent is from about 3 to about 10 grams per liter of solution and optimum results are obtained with about 5 grams per liter of solution. The polyamino-polyacetic acids, i.e. acids containing two or more amino groups and two or more acetic acid radicals, are well known sequestering agents. Illustrative examples of these acids include:

ethylenediamine tetraacetic acid,

diethylenetriamine pentaacetic acid,

ortho-diamine cyclohexane tetraacetic acid, ethyleneglycol bis(aminoethyl ether) tetraacetic acid, diaminopropanol tetraacetic acid, N-(Z-hydroxyethyl)ethylenediamine triacetic acid,

and the like. For incorporation as sequestering agents in the cleaning solution of this invention, the acids may be employed as suchv or in the form of a salt, e.g. in a form in which one or more of the carboxyl groups have formed a salt with an alkali metal ion. Thus, for example, the tetra sodium salt of ethylene diamine tetraacetic acid, which is very commonly employed as a sequestering agent, may be used in formulating the cleaning solution.

(7) A strong inorganic base in a sufiicient amount that the pH of the cleaning solution is in the range from about 6 to about 8, more preferably in the range from about 6.5 to about 7.5, and most preferably about 7. Examples of strong inorganic bases that may be utilized are alkali metal hydroxides, such as sodium hydroxide or potassium hydroxide, and alkali metal carbonates such as sodium carbonate or potassium carbonate.

Each of the ingredients specified hereinabove performs an important function in the cleaning solution. Thus, the ferricyanide serves to bleach the metallic silver, i.e. oxidize metallic silver to silver ion, and also acts to soften the gelatin. The thiocyanate acts to form a soluble complex of silver and promotes the function of the ferricyanide. It also acts as a gelatin softening agent. The dichromate serves to improve the stability of the solution and thereby prolong the useful life of the cleaner. The nitrate acts as a corrosion inhibitor and thereby permits the cleaning solution to be used without harming the equipment. The citrate serves as a gelatin softening agent and promotes the removal of hard water salts. The polyaminopolyacetic acid sequestering agent functions to remove hard water salts by formation of soluble complexes. The strong inorganic base is utilized to form a solution with an initial pH within the range needed for stability, as hereinbefore described.

The novel cleaning solutions of this invention exhibit excellent stability characteristics so that they may be used repeatedly to clean equipment until they become exhausted. However, the activity of the solution, i.e. its ability to remove silver-containing deposits, deteriorates with time so that the solution is preferably formulated immediately prior to use. The life span of the solution may extend for a period of several days to several weeks from the time it is prepared depending on the extent of use. When the solution has reached a stage of exhaustion, it becomes dark blue or black in color, probably as a result of formation of Prussian Blue or Turnbulls Blue. Solution stability is primarily affected by the initial pH and the balance between the levels of dichromate, citrate, and polyaminopolyacetic acid sequestering agent. Thus, if the dichromate level is too low, or the levels of citrate and/or polyaminopolyacetic acid sequestering agent are too high, the solution will be unstable. Instability is characterized by the evolution of gas and a rapid decrease in the ability of the solution to remove silver-containing deposits. Also, with an unstable solution there will be a rapid drop in pH upon use, sometimes to a level as low as 4 or less, whereas the optimum formulation described herein usually undergoes a slight increase in pH upon use, e.g. an increase from a pH of 7 to about 7.5.

In view of the fact that the activity of the cleaning solution deteriorates on standing, it will not ordinarily be feasible to package it as a complete formulation and it will usually be necessary to package it as a two part system with instructions to mix the two parts together immediately prior to use. The parts to be mixed may be packaged as dry powders or as liquids, as desired. One suitable method of packaging is to package the thiocyanate separately in the form of an aqueous solution and the remaining ingredients together as a blend of dry powders. In this instance, an alkali metal carbonate is advantageously employed as the strong inorganic base as it is readily available in powder form. An alternative system of packaging is to formulate two aqueous solutions which are mixed together immediately prior to use. The first solution would contain the ferricyanide, the dichromate and the nitrate, while the second solution would contain the thiocyanate, the citrate, the polyaminopolyacetic acid sequestering agent, and the strong inorganic base. In this case, it is feasible to use an alkali metal hydroxide as the strong inorganic base in place of the carbonate.

The cleaning solution of this invention may be used in any of several different ways to eifect cleaning of photographic processing equipment. Thus, for example, the equipment to be cleaned may be soaked for several hours in a bath of the cleaning solution and any remaining residue wiped away. To promote cleaning, the solution may be heated and/or stirred. Brushing and/or scraping may be utilized together with or subsequent to washing of the equipment with the cleaning solution.

It will usually be worthwhile from a cost standpoint to recover the silver from the spent cleaning solution. A suitable method for accomplishing such recovery is to add sodium hydrosulfite to the spent solution to precipitate a sludge comprised of silver and silver sulfide and then smelt the sludge to recover the silver. An alternative method is to dilute the spent celaning solution with an equal volume of an acidic fixing solution and then recover the silver by the technique of metallic replacement by bringing the mixture into contact with a metal which is more electropositive than silver, e.g. iron or zinc, so as to effect replacement of the dissolved silver. This method may be conveniently and inexpensively accomplished using steel wool as the metal and employing the apparatus described in U.S. Pat. 3,369,801.

As a specific illustration of the present invention, a cleaning solution with a pH of 7 was prepared by dissolving in one liter of water the following ingredients:

grams of potassium ferricyanide grams of ammonium thiocyanate 10 grams of potassium dichromate 30 grams of sodium nitrate 10 grams of sodium citrate 5 grams of the tetra sodium salt of ethylene diamine tetraacetic acid, and

6 grams of sodium carbonate monohydrate.

This solution was used in cleaning Itek Positive Process equipment utilized in processing Photostat Photocopy Paper, Type PPO, and was found to be effective in removing silver-containing deposits from the racks taken from the developing, wash-off and wash tanks. On the racks from the developing tanks, the deposit is principally metallic silver and gelatin together with minor amounts of calcium and magnesium phosphates. On the racks from the wash-off and wash tanks, the deposits are largely comprised of photographic emulsion which has adhered and hardened. They consist chiefly of gelatin and hard water salts together with a minor amount of metallic silver. The cleaning solution was also used with good results in cleaning Recordak Reader-Printers and in cleaning the rollers from Kodak Viscomat Processors. In these instances, the deposits consist primarily of metallic silver.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. A cleaning solution for removal of silver-containing deposits from photographic processing equipment, said cleaning solution consisting essentially of an aqueous solution of (1) a member selected from the group consisting of ammonium ferricyanide and alkali metal ferricyanides in a concentration of from about 40 to about 200 grams per liter of solution,

(2) a member selected from the group consisting of ammonium thiocyanate and alkali metal thiocyanates in a concentration of from about 40 to about 200 grams per liter of solution,

(3) a member selected from the group consisting of ammonium dichromate and alkali metal dichromates in a concentration of from about 2 to about 25 grams per liter of solution,

(4) a member selected from the group consisting of ammonium nitrate and alkali metal nitrates in a concentration of from about 10 to about 60 grams per liter of solution,

(5) a member selected from the group consisting of ammonium citrate and alkali metal citrates in a con centration of from about 2 to about 25 grams per liter of solution,

(6) a polyaminopolyacetic acid sequestering agent in a concentration of from about 2 to about 20 grams per liter of solution, and

(7) a sufiicient amount of a strong inorganic base to provide a solution pH in the range of from about 6 to about 8.

2. A cleaning solution for removal of silver-containing deposits from photographic processing equipment, said cleaning solution consisting essentially of an aqueous solution of (l) a member selected from the group consisting of ammonium ferricyanide and alkali metal ferricyanides in a concentration of from about 60 to about 100 grams per liter of solution,

(2) a member selected from the group consisting of ammonium thiocyanate and alkali metal thiocyanates in a concentration of from about 100 to about 140 grams per liter of solution,

(3) a member selected from the group consisting of ammonium dichromate and alkali metal dichromates in a concentration of from about to about grams per liter of solution,

(4) a member selected from the group consisting of ammonium nitrate and alkali metal nitrates in a concentration of from about to about 40 grams per liter of solution,

(5) a member selected from the group consisting of ammonium citrate and alkali metal citrates in a concentration of from about 5 to about 15 grams per liter of solution,

(6) a polyaminopolyacetic acid sequestering agent in a concentration of from about 3 to about 10 grams per liter of solution, and

(7) a sufiicient amount of a strong inorganic base to provide a solution pH in the range of from about 6.5 to about 7.5.

3. A cleaning solution as described in claim 2 wherein said sequestering agent is the tetra sodium salt of ethylenediamine tetraacetic acid.

4. A cleaning solution as described in claim 2 wherein said inorganic base is an alkali metal hydroxide.

5. A cleaning solution as described in claim 2 wherein said inorganic base is an alkali metal carbonate.

6. A cleaning solution for removal of silver-containing deposits from photographic processing equipment, said cleaning solution consisting essentially of an aqueous solution of (l) a member selected from the group consisting of ammonium ferricyanide and alkali metal ferricyanides in a concentration of about 80 grams per liter of solution,

(2) a member selected from the group consisting of ammonium thiocyanate and alkali metal thiocyanates in a concentration of about 120 grams per liter of solution,

(3) a member selected from the group consisting of ammonium dichromate and alkali metal dichromates in a concentration of about 10 grams per liter of solution.

(4) a member selected from the group consisting of ammonium nitrate and alkali metal nitrates in a concentration of about 30 grams per liter of solution,

(5) a member selected from the group consisting of ammonium citrate and alkali metal citrates in a concentration of about 10 grams per liter of solution,

(6) a polyaminopolyacetic acid sequestering agent in a concentration of about 5 grams per liter of solution, and

(7) a sufiicient amount of a strong inorganic base to provide a solution pH of about 7.

7. A cleaning solution for removable of silver-containing deposits from photographic processing equipment, said cleaning solution consisting essentially of an aqueous solution of (1) potassium ferricyanide in a concentration of about grams per liter of solution,

(2) ammonium thiocyanate in a concentration of about grams per liter of solution,

(3) potassium dichromate in a concentration of about 10 grams per liter of solution,

(4) sodium nitrate in a concentration of about 30 grams per liter of solution,

(5) sodium citrate in a concentration of about 10 grams per liter of solution,

(6) the tetra sodium salt of ethylenediamine tetraacetic acid in a concentration of about 5 grams per liter of solution, and

(7) sodium carbonate monohydrate in a concentration of about 6 grams per liter of solution.

References Cited UNITED STATES PATENTS 3,080,323 3/1963 Newman 252l03 3,098,043 7/1963 Wendell, Jr. 252-103X MAYER WEINBLATT, Primary Examiner US. Cl. X.R. 96-50 

